On negative evidence, Orthisina, Theca, Producta, or Spirifer are believed not to exist in the present seas: on negative evi dence the existing genera of siplionated bivalves and univalves are deemed to have been very rare in permian, triassic, or oolitic times. To suspect that they may have then abundantly existed, but have hitherto escaped observation, because certain Lamellibranchs with an open mantle, and some holostomatous and asiphonate Gastropods, have left their remains in secondary strata, is not more reasonable, as it seems to me, than to con clude that the proportion of mammalian life may have been as great in secondary as in tertiary strata, because a few small forms of the lowest orders have made their appearance in triassic and oolitic beds.
Turning from a retrospect into past time for the prospect of time to come, I may crave indulgence for a few words, of more sound, perhaps, than significance, relative to the amount of prophetic insight imparted by Palaeontology. But the re flective mind cannot evade or resist the tendency to speculate on the future course and ultimate fate of vital phenomena in this planet. There seems to have been a time when life was not; there may, therefore, be a period when it will cease to be.
Our most soaring speculations still show a kinship to our nature : we see the element of finality in so much that we have cognizance of, that it must needs mingle with our thoughts, and bias our conclusions on many things.
The end of the world has been presented to man's mind under divers aspects : as a general conflagration; as the same, preceded by a millennial exaltation of the world to a paradisiacal state,—the abode of a higher race of intelligences.
If the guide-post of Palaeontology may seem to point to a course ascending to the condition of the latter speculation, it points but a very short way, and in leaving it we find ourselves in a wilderness of conjecture, where to try to advance is to find ourselves " in wandering mazes lost." With much more satisfaction do I return to the legitimate deductions from the phenomena which have been under review. In the survey which has been taken of the various forms of life that have passed away—of their characters, succession, logical position, and geographical distribution—if I have suc seeded in demonstrating the adaptation of any structure to the exigencies, habits, and well-being of the species, I have fulfilled one object which 1 had in view, viz., to set forth the beneficence and intelligence of the Creative Power.
If, iu all the striking changes of form and proportion which have passed under review, we could discern only the results of minor modifications of a few essential elements, we must be the more strikingly impressed with the unity of that Cause, and with the wisdom and power, which could produce so much variety, and at the same time such perfect adaptations and en dowments, out of means so simple. For, in what have those
contrasted limbs, hoofs, paws, fins, and wings, so variously formed to obey the behests of volition in denizens of different elements, differed from the mechanical instruments which we ourselves plan with foresight and calculation for analogous uses, save in their greater complexity, in their perfection, and in the unity and simplicity of the elements which are modified to constitute these several locomotive organs Everywhere in organic nature we see the means not only subservient to an end, but that end accomplished by the simplest means. Hence we are compelled to regard the Great Cause of all, not like certain philosophic ancients, as a uniform and quiescent mind, as an all-pervading anima mundi, but as an active and anticipating intelligence.
By applying the laws of comparative anatomy to the relics of extinct races of animals contained in and characterizing the different strata of the earth's crust, and corresponding with as many epochs in the earth's history, we make an important step in advance of all preceding philosophies, and are able to demonstrate that the same pervading, active, and beneficent intelligence which manifests His power in our times, has also manifested His power in times long anterior to the records of our existence.
But we likewise, by these investigations, gain a still more important truth, viz., that the phenomena of the world do not succeed each other with the mechanical sameness attributed to them in the cycles of the epicurean philosophy; for we are able to demonstrate that the different epochs of the earth were attended with corresponding changes of organic structure; and that, in all these instances of change, the organs, still illustra ting the unchanging fundamental types, were, as far as we could comprehend their use, exactly those best suited to the functions of the being. Hence we not only show intelligence evoking means adapted to the end ; but, at successive times and periods, producing a change of mechanism adapted to a change in external conditions. Thus the highest generalizations in the science of organic bodies, like the Newtonian laws of universal matter, lead to the unequivocal conviction ,of a great First Cause, which is certainly not mechanical.